The core of step #2 of the solution is the BW or BrokenWing/Oddagon at (6)r1c48, r5c8, r6c49 (marked by *). This is a potential 5-sided loop of conjugate links of 6s which would be impossible if it existed by itelf. There are three 6s called 'Guardians' (marked by G above) at r4c45 and r5c9 that prevent that pattern. Thus, if guardian (6)r5c9 is not true then guardians (6)r45c4 must be true and vice-versa.

Of interest also: The BW pattern actually eliminates (6)r5c5 immediately because if it were true, it would eliminate all 3 guardians which can't happen. This is interesting because it is rare to find immediate BW eliminations in more complicated puzzles. BTW: Since the chain eliminates both 6s at r45c5 anyway, it isn't necessary to add this as a separate step.